The present invention relates to implantable devices, and more particularly, to a fully implantable device or system for stimulating or sensing living tissue. The implantable device includes a rechargeable battery or other replenishable power source. More particularly, the present invention relates to a fully implantable cochlear implant system (FICIS) that allows profoundly deaf persons to hear sounds without the need for wearing or carrying external (non-implanted) hearing devices or components.
Presently available implantable stimulation devices, such as a cochlear implant device or a neural stimulator, typically have an implanted unit, an external ac coil, and an external control unit and power source. The external control unit and power source includes a suitable control processor and other circuitry that generates and sends the appropriate command and power signals to the implanted unit to enable it to carry out its intended function. The external control unit and power source are powered by a battery that supplies electrical power through the ac coil to the implanted unit via inductive coupling for providing power for any necessary signal processing and control circuitry and for electrically stimulating select nerves or muscles. Efficient power transmission through a patient""s skin from the external unit to the implanted unit via inductive coupling requires constant close alignment between the two units.
Representative prior art cochlear implant systems are disclosed, e.g., in U.S. Pat. Nos. 4,532,930; 4,592,359; 4,947,844; 5,776,172; and 6,067,474, all of which are incorporated herein by reference.
Disadvantageously, each of the known prior art cochlear stimulation systems, with the exception of some embodiments of the system disclosed in the U.S. Pat. No. 6,067,474, requires the use of an external power source and speech processing system, coupled to the implanted stimulation device. For many patients, achieving and maintaining the required coupling between the external components and the implanted component can be troublesome, inconvenient, and unsightly. Thus, there exists a need and desire for a small, lightweight fully implantable device or system that does not require an external unit in order to be fully functional, that does not need constant external power, and that includes a long-lasting internal battery that may be recharged, when necessary, within a relatively short time period.
Moreover, even if a rechargeable battery were available for use within an implantable cochlear stimulation system, such rechargeable battery must not significantly alter the size of the existing implantable cochlear stimulator. This is because the curvature and thickness of the skull is such that there is only a limited amount of space wherein a surgeon may form a pocket wherein a cochlear stimulator may be implanted. This is particularly an acute problem for young children, where the thickness of the skull is relatively thin and the curvature of the skull is greater than for an adult. Thus, there is a need for a fully implantable cochlear implant system that is adaptable and lends itself for implantation within a range of head sizes and shapes.
Additionally, even where a rechargeable battery is employed within a fully implantable cochlear implant system, which fully implantable system includes an implantable speech processor and microphone, it may be necessary or desirable, from time to time, to replace the battery and/or to upgrade the speech processor hardware. Because implantation of the cochlear implant system, including insertion of the delicate electrode array into the cochlea of the patient, represents major surgery, which major surgery would hopefully only need to be performed once in a patient""s lifetime, it is seen that there is also a need for a fully implantable cochlear implant system wherein at least the battery, and perhaps even some or all of the speech processing circuitry, may be replaced or upgraded from time to time through minimal invasive surgery, while leaving the delicate cochlear electrode array intact for use with the replaced battery and/or upgraded speech processor.
The present invention addresses the above and other needs by providing a fully implantable cochlear prosthesis that includes (1) an implantable hermetically sealed case wherein electronic circuitry, including an implantable microphone, are housed, (2) an active electrode array that provides a programmable number of electrode contacts through which stimulation current may be selectively delivered to surrounding tissue, and (3) a connector that allows the active electrode array to be detachably connected with the electronic circuitry within the sealed case.
In accordance with one aspect of the invention, the active electrode array provides a plurality of groups of electrodes, each electrode having both medial and lateral contacts, any one of which may be selected to apply a stimulus pulse through active switching elements included within the array, preferably through the use of Stimulation Groups.
In accordance with another aspect of the invention, the active switching elements included within the array operate at a very low compliance voltage, thereby reducing power consumption.
In accordance with still another aspect of the invention, radial stimulation may be provided by the active electrode array in order to increase selectivity.
In accordance with yet another aspect of the invention, the entire prosthesis is very efficient from a power consumption standpoint, thereby allowing a smaller battery to power the system for longer periods of time before recharging or replacement is required.
In accordance with a further aspect of the invention, the hermetically sealed case within which the electronic circuitry, battery, and microphone are housed may be replaced, when needed, through minimally invasive surgery.
In accordance with an additional aspect of the invention, the electronic circuitry housed within the hermetically sealed case may be programmed or adjusted, e.g., upgraded, as needed, using either RF or acoustic control signals received through an implantable coil or an implantable microphone. In a preferred embodiment, acoustic control signals are realized using phase-shift keyed (PSK) modulation of an acoustic signal within a very narrow band centered at about 6 KHz.
It is thus an object of the present invention to provide a fully implantable tissue stimulation prosthesis that utilizes an active electrode array.
It is another object of the invention to provide such a fully implantable prosthesis that includes both digital and analog circuits, any one or all of which may be used depending upon the selected mode of operation